1. Field of the Invention
The present invention relates to load-connection-state detector circuits and more particularly to a load-connection-state detector circuit that can correctly detect connection-state of loads with a simplified construction. Description of the Prior Art
A stereo amplifier as shown in FIG. 1 is previously known in which a first input amplifier circuit 1 and first and second output amplifier circuits 2 and 3 make up a left-channel amplifier 4 so that a left-channel stereo signal derived from a first signal source 5 is applied from the left-channel amplifier to a left-channel speaker 6 that makes a load and in which, in contrast, a second input amplifier circuit 7 and third and fourth output amplifier circuits 8 and 9 make up a right-channel amplifier 10 so that a right-channel stereo signal derived from a second signal source 11 is applied from the right-channel amplifier 10 to a right-channel speaker 12.
In the stereo amplifier, output signals opposite in phase to each other generated by the first and second input amplifier circuits 1 and 7 are applied to the first to fourth output amplifier circuits 2 to 9, which circuits thus BTL-drive left-channel and right-channel speakers 6 and 12, respectively.
When the foregoing stereo amplifier is used as on-vehicle equipment, the left-channel and right-channel speakers 6 and 12 are embedded into a panel of a car. This prohibits visual verification of whether or not the stereo amplifiers are correctly connected with the speakers, so that it is required to listen to sounds produced by the speakers with input signals applied, by ear. In noisy places such as in factories, however, the aural check is difficult to carry out and, for more accuracy, requires a lot of time. This problem has been growing remarkably in recent days as the speakers provided in a car increases in number.